In the field of cancer chemotherapy, many compounds have already been put to practical use as medicine. However, their effects on various kinds of tumors are not necessarily adequate, and further the problem of resistance of tumor cells to these drugs makes the methods of clinical use thereof complicated [refer to Proceedings of the Japanese Cancer Association, 47 Annual Meeting, pages 12 to 15 (1988)].
In such state of things, development of novel carcinostatic substances is always desired in the field of cancer therapy. Particularly, substances are necessitated which overcome resistance of tumor cells against existing carcinostatic substances and exhibit effectiveness against such kinds of cancers that existing carcinostatic substances cannot exert adequate effects thereon.
In the light of such present state of things, the present inventors widely screened microbial metabolic products, as a result, found a novel antitumor activity-possessing compound BE-13793C (12,13-dihydro-1,11-dihydroxy-5H-indolo[2,3-a]pyrrolo[3,4-c]carbazole-5,7( 6H)-dione), and disclosed it in the preceding patent application (Japanese Patent Application No. 71149/1989).
Further, the present inventors synthesized derivatives of BE-13793C, found that novel compounds represented by the later-described general formula (I) exhibited an excellent antitumor action, and completed this invention.